Start building against snapshots for Spring Framework 5.2.0.M3

See gh-16963

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -179,7 +179,7 @@
 		<snakeyaml.version>1.24</snakeyaml.version>
 		<solr.version>8.0.0</solr.version>
 		<!-- deprecated in favor of "spring-framework.version" -->
-		<spring.version>5.2.0.M2</spring.version>
+		<spring.version>5.2.0.BUILD-SNAPSHOT</spring.version>
 		<spring-amqp.version>2.2.0.M2</spring-amqp.version>
 		<spring-batch.version>4.2.0.M2</spring-batch.version>
 		<spring-cloud-connectors.version>2.0.5.RELEASE</spring-cloud-connectors.version>